Study On Mechanical Properties Of Sand Loess Modified By Cement Under Freeze-thaw Condition

Northwestern China belongs to the typical seasonal frozen soil area,and packing the lack of A,B group,the soil along with the change of season will undergo at least once A year freezing and melting freezing and thawing,the railway subgrade in affected by freeze-thaw action due to seasonal change happen at the same time,also will be produced by the load as the train passed,appear such as frost heave thawing settlement,uneven settlement and so on,causing serious pollution of railway train driving safety.With the development of the railway in northwest China and the increasing speed of trains,the deformation requirements of railway foundation and roadbed become more demanding.Therefore,it is very urgent to solve the problems such as the lack of quality packing and the research on the packing with good freeze-thaw performance.However,there are relatively few studies on the stability of roadbed under the double action of freeze-thaw and train cycle load.On the basis of relevant domestic and foreign studies,this paper studied the influence of factors such as the number of freezing-thawing cycles,test confining pressure and freezing temperature on the strength and deformation characteristics of the cement improved soil by taking the cement improved sand loess with the content of 6% as the research object.The main results are as follows:(1)Through a series of geotechnical tests,the basic physical and mechanical properties of cement improved soil were studied,and the unconfined compressive strength of cement improved soil with different incorporation ratio and the failure form of cement improved soil were obtained,and the optimal content of cement improved soil was determined to be 6%.(2)According to the standard triaxial test,the stress-strain relationship and strength index of the cement modified soil are affected by freezing-thawing cycle times,freezing temperature,confining pressure and other factors to different degrees,and the influence of freezing-thawing cycle on the static strength,shear strength index and initial tangent modulus of the cement modified soil is analyzed.(3)The constitutive model of cement modified soil under freeze-thaw condition based on Duncan-Chang model is analyzed.(4)By means of GDS dynamic triaxial test in laboratory,the variation rules of the cumulative plastic strain and critical dynamic stress of cement soil under different factors such as the number of freezing-thawing cycles,test confining pressure and dynamic stress amplitude were studied.The range of critical dynamic stress is determined.(5)The dynamic stress-strain relationship and dynamic strength of cement soil under freeze-thaw condition were analyzed.Based on the hardin-drnevich hyperbolic model,the dynamic stress-strain test data of cement modified soil were analyzed and fitted.